Process of brominating indigo.



UNITED s'rATEs PATENT OFFICE.

ALBRECHT SCHMIDT, OF HOCHST-ON-THE-MAIN, GERMANY, ASSIGNOR TO FARBWVERKE, VORM. MEISTER, LUCIUS & BRIINING, OF HOOHST-ON: THE-MAIN, GERMANY, A CORPORATION OF GERMANY.

PROCESS OF BROIVIINATING YINDIGO.

Specification of Letters Patent.

, Patented Dec. 19, 1905.

Application filed October 17, 1902. Serial No. 127,722.

To all whom it may concern:

Be it known thatI, ALBRECHT SCHMIDT, Ph. D., a citizen of the Empire of Germany, residing at H6c11st-on-the-Main, Germany, have invented certain new and useful Improvements in the Manufacture of Bromo-Substitution Products of Indigo, of which the following is a specification.

According to the German Patent No. 12,875 indigo can be brominated only in the absence of water. In fact, large quantities of bromoisatin are obtained if an aqueous indigo paste of twenty-per-cent. strength is brought together with bromin, as already observed by Erdmann.

I have found that indigo may also be brominated even in the presence of water if the action of bromin on indigo occurs in the presence of inorganic acids-especially, for instance, with sulfuric, hydrochloric, hydrobromic, or fluoric acids. The quantity and strength of these acids, however, has to be controlled to avoid as much as possible any formation of bromo-isatin. I have found that by employing certain concentrations varying according to the choice of the inorganic acids the bromination will occur smoothlythat is to say, without or with hardly any formation of bromo-isatin. If a lower degree of concentration is used, the yield of bromo-indigo decreases, whereas the bromo-isatin increases. In the case of hydrobromic acid instead of adding it at the beginning it may also be allowed to form during the process of substitution by brominating indigo in water. Of course it is necessary here to use only little waterfor instance, instead of an indigo paste of twenty-per-cent. strength indigo moistened only with twenty to fifty per cent. of water-for otherwise the hydrogen bromid formed during the process of substitution would not suffice to produce at the beginning the more concentrated hydrobromic acid favorable for bromination. The same holds good if dilute inorganic acids are used,which when employed in great quantities do not produce a favorable result of bromination; but when used, as in the case with little water, preferably in the presence of solid or liquid indifferent diluents, a very good product of bromination may yet be arrived at.

According to the quantity of bromin employed more or less highly brominated products may be obtained. It is best not to exceed the quantity of bromin of four atoms, so that a di-product of substitution may be ob: tained; but the less brominated products (calculated, for instance, to monobromo-indigo) are also very valuable and even higher than di-brominated products may be employed. As inorganic acids are to be considered in the first place sulfuric, hydrochloric, hydrobromic, and fluoric acids, phosphoric acid is only suitable if the operation is carried on with very little water. Its action is inferior to that, for example, of sulfuric or hydrobromic acid. Also acid inorganic salts may be employed in the latter sense. The usual carriers may be added during bromination. The following eX- amples illustrate the bromination:

a. Bromination in Sulfuric Acid.

The process may be carried out in different ways. It is known that indigo with sulfuric acid of about seventy-eight per cent. strength forms an indigo sulfate, which on more water being added is decomposed again into sulfuric acid and indigo. The bromination may therefore take place in sulfuric acid of such concentration that indigo sulfate is still formed for instance, sulfuric acid of seventy-eight per cent. strength or in somewhat more dilute sulfuric acid, so that the indigo sulfate formed is again decomposed into indigo and sulfuric acid. In the latter case, however, it is preferable not to use sulfuric acid essentially below fifty per cent. strength, for otherwise considerable quantities of bronlo-isatin will be the result. Finally, though less advantageous, a more concentrated sulfuric acid than of seventy-eight per cent. strength may be used, care having to be taken that no sulfonation of indigo occurs. It is best, there- Stirring is contin ing.

stance, are allowed to run in.

The brominated indigo thus formed may be separated by filtration or subsequent wash- The brominated indigo obtained in this manner contained, for instance, about twentyfive per cent. of bromin and very small quantities of bromo-isatin. It is a blue powder of violet shade soluble in concentrated sulfuric acid with a yellowish-green color, which on standing turns blue. In boiling anilin the product of bromination dissolves only with great difliculty to a blue color. Pyridin dissolves it likewise, only very sparingly, amylalcohol not at all, and nitrobenzene somewhat when in a state of ebullition with a blue color.

Example II: To obtain higher brominated products, the operation is the same as in Example I. Only one hundred and forty to one hundred and sixty parts of bromin, for in- The product of bromination obtained from one hundred and forty or one hundred and sixty parts of bromin dyes even clearer than that obtained from ninety parts of bromin. The product obtained from one hundred and forty parts of bromin contained, for instance, about thirtytwo per cent. of bromin. It is a blue powder of violet shade and dissolves in sulfuric acid to a bluish-green color, which on standing turns into blue. Its behavior toward anilin, pyridin, amyl-alcohol, and nitrobenzene is the same as that described in Example I. Very good results are also obtained with somewhatdiluted sulfuric acidfor instance, of about seventy per cent. strength, still capable of forming indigo sulfate. Moreover, small quantities of hydrobromic acid, (NaBr,FeBr2,) &c., may be added to the sulfuric acid to start the bromination. This addition, however, is not necessary if the bromin is introduced slowly. The quantity of sulfuric acid to be employed may Vary according to requirement Bromimtltioii in JIfore Dilute SulfuricAcicl,

so that no Indigo Sulfate Orm Ewist.

Example IV: 35.2 parts of indigo are introduced into three hundred parts of sulfuric acid of seventy-eight per cent, so that a uniform indigo-sulfate paste is formed. The mixture is then slowly diluted with about ninety to one hundred and ten parts of water or dilute hydrobromic acid, when the indigo sulfate mostly decomposes into finely-divided indigo and sulfuric acid, whereupon forty-two parts of bromin are gradually introduced with stirring. If after stirring for sometime the bromin has completely disappeared, the liquid is then poured into water, fitered, and washed.

Example V: If a less brominated product is to be obtained in the manner described in Example IV, then correspondingly less brominfor instance, fifteen, twenty, twentyfour, 620., parts of itare employed, when the product obtained will contain more or less unchanged indigo. Instead of dilute sulfuric acid also a mixture of acid alkali sulfates with sulfuric acid may be used, or. though less advantageous, a mixture of acid alkali sulfates alone with little water or a mixture of sulfurc and hydrobromic acid or hydrochloric aci b. Bromimttion in Hydrochloric 07 Hydrobromio Acid (mtl Fluoric Acicl.

Example I: One hundred and thirty-one parts of finely-divided indigo, are stirred together with about six hundred parts of concentrated hydrochloric acid of thirty-six-percent. strength, about ninety parts of bromin being gradually added at 10 to 15 centigrade while cooling and stirring. 'When all bromin has disappeared, the mixture is diluted with water, filtered, and washed. Instead of concentrated hydrochloric acid, for instance, hydrochloric acid of thirty per cent. may be employed, when it is better, however, to use less liquid.

Example II: In the above example for hydrochloric acid may be employed, for instance, hydrobromic acid of about forty-percent. strength or more or fluor acid, the operation being otherwise the same.

Example III: To obtain higher brominated I 0. Bromimttion in Little IVclter. IVit/t Bromimltion in Little lVrtter it is Best to Employ Solicl 01" LiquiclDiluents.

Example I: One hundred and seventy-six parts of finely-divided indigo are stirred with fifty parts of water, two hundred and twenty parts of bromin, preferably in the form of gas, being allowed to gradually act thereon. Cooling will have to be recurred to if the bromin is not introduced very slowly. The moist indigo may also be stirred with indifl'erent agents-such as gravel, benzene, &c.to permit of better stirring or mixing. On completion of the reaction the mixture is stirred with water or ammonia or with a liquid of alkalin reaction. It is then filtered and dried.

If less bromin than stated is employed for instance, one hundred parts of bromina less brominated product will be obtained.

The brominated indigoes obtained according to a, Z), and 0 resemble in their tinctorial properties those obtained by dry bromination as set forth in German Patent No. 128,57 5; but whether they are identical with the latter or with that obtained syntheticallyfor instance, from indoxyl, &c. (di-bromo indigo) could hitherto not be observed.

Of course the hydrogen bromid formed during the substitution may be used again for the substitution. Thus the whole of the bromin employed during the process of substitution may be utilized, even in a single operation, by liberating the bromin from the hydrogen bromid formed by means of known agentsfor example, by adding a hypochlorite, a chlorate, or a bromate-preferably by previously adding a little hydrochloric acid; also, for instance, by carefully introducing dilute chlorin gas or a liquid containing chlorin during or after having poured in the bromin or bromate.

The bromin from the hydrogen bromid resulting from the process of substitution may also be liberated by electrolysis with or without diaphragm, the action of the electrolytical hydrogen on bromo-indigo in an acid solution being not essential provided the abovementioned conditions are adhered to.

Having now described my invention, what I claim is 1. The herein-described process of brominating indigo, which consists in treating indigo with bromin in the presence of an aqueous halogen acid of such concentration as to permit of the least possible formation of bromoisatin.

2. The herein-described process of brominating indigo, which consists in subjecting a mixture of indigo and about twenty to fifty per cent. of water, to the action of bromin, whereby aqueous hydrobromic acid is formed, and subjecting said indigo to the action of said hydrobromic acid.

In testimony that I claim the foregoing as my invention I have signed my name in presence of two subscribing witnesses.

ALBRECHT SCHMIDT.

Witnesses:

ALFRED BRIsBoIs, J OHANN HARTENSTEIN. 

